In the last decades, the increase in the demand of fuels has caused a decrease in the reserves of light crudes throughout the world. As a consequence, there has been an increase in the production and availability of heavy crudes, causing an increase in the research to make better use of heavy crude oil.
The low yields of light distillates recovered from the heavy crudes as well as the need to reduce the high levels of contaminants such as sulfur, nitrogen asphaltenes carbon and metals (Ni and V) have oriented the research efforts towards the hydrotreatment processes with the aim of improving the properties of heavy feeds.
At present, the environmental restrictions throughout the world have made mandatory the search for more effective catalysts in order to obtain better quality fuels with a minimum content of polluting agents like sulfur and nitrogen.
The catalysts used for hydrotreating of residua and heavy crudes are an interesting alternative to remove impurities such as sulfur, metals, asphaltenes, etc., and to increase notably the production of middle distillates. In this sense the formulation of the catalyst involves the control of its properties, the interaction of the active components with the support, and the method of preparation. The methodology of incorporation of the active phases or composition of the support can change the activity and stability of the catalyst. At present there are few reports in the literature that directly refer to the hydrotreatment of heavy crudes and residua; the studies have rather focused on the treatment of residua obtained from light or medium heavy crudes.
The majority of patents relating to the present invention claim the use of metals of groups VIB and VIII of the periodic table, supported on alumina. Likewise, other patents claim the use of Mo with Ni and/or Co. Several others include the use of compounds based in the elements of groups IA, IIA, VA, VIIA, IIB, IVB, VB and VIIB of the periodic table using different types of supports such as alumina, zeolites, silica, silica-alumina, magnesium, silica-magnesium, titanium, activated carbon, clays, alumina-boron, zirconium and combinations of them. Some of these patents are described below.
U.S. Pat. No. 4,687,757 discloses an alumina support which can contain compounds of transition metals from the groups IB, VB, VIB, VIIB and the VIII of periodic table, the support contains at least one compound of titanium and one of molybdenum, having a surface area in the 100-250 m2/g interval. In the detailed description of the patent, a pore volume of 0.2-2.0 cm3/g is mentioned, which was determined in a mercury penetration equipment, used to determine macro-porosity, as demonstrated in example 1, in the preparation of the catalyst D having pore volume 1.03 cm3/g. From these data, it is evident that the catalyst of the referred patent is used mainly in the hydrodemetallization stage and not in the hydrodesulfurization stage.
U.S. Pat. No. 5,545,602 discloses a catalyst with a composition containing 13-24 weight % of metals of group VIII, 0-2 weight % of metals of group VIB and one phosphorus oxide, with a surface area of 150-240 m2/g, total pore volume of 0.7-0.98 cm3/g, and a pore volume distribution where less than 20% corresponds to the micro-pore zone with diameter of 100 Å (10 nm), around 34-74% corresponds to pores within the 100-200 Å interval (10-20 nm), from 26-46% corresponds to the region of meso-pores with pore diameter of 200 Å (20 nm), 22-32% with pore diameters of 250 Å (25 nm), and the macro-pore region with diameters of 1,000 Å (100 nm) contributes with 14-22%. This catalyst is used mainly for residua feedstock having 4-6° API gravity.
Chinese Patent No. 1,552,520 claims a catalyst for the hydrodesulfurization of hydrocarbons which consists of a support of gamma alumina with titania and active metals of groups VIB and VIII. A mixture of dry aluminum hydroxide and titanium dioxide (TiO2) powder. To this mixture an alkaline solution containing molybdenum and/or tungsten is added.
U.S. Pat. No. 6,218,333 discloses a detailed method for the preparation of a catalyst by means of a porous support (alumina, silica-alumina, silica, titanium, boron, zeolites, zirconium, magnesium and their combinations) with one or more active metals (Mo, W, Co, Ni and their oxides, sulfides and mixtures of them). This results in an initial catalytic prototype which contains volatile compounds. Later, the concentration of these volatile compounds is diminished by means of an ex-situ or in situ reduction stage. The catalyst is used for the hydrotreating of hydrocarbon feedstocks.
The patent WO 0,253,286 claims a hydroprocessing catalyst for the conversion of the heavy oil hydrocarbons, which contains a transition metal of group VI in a concentration of 7 to 20 weight % and a metal of group VIII in a concentration of 0.5-6 weight %, calcined to obtain the corresponding oxide over a support of alumina. The resultant catalyst has 100 to 180 m2/g specific surface area and total pore volume of 0.55 cm3/g or higher. The catalyst lowers the metals contained in heavy hydrocarbons and enhances the elimination of asphaltenes, sulfur, nitrogen and Conradson carbon, besides, the catalyst shows a decrease in the formation of sediments and better conversion in ebullated bed operations. In fixed bed operation a product with improved stability for its storage is obtained. A hydroprocessing of heavy hydrocarbon feedstock with the catalyst in fixed or ebullated bed is disclosed.